Technical Abstract:
Pseudomonas fluorescens strain Q2-87 showed significant antagonistic activity against the damping-off pathogens of slash pine (Pinus elliottii), including Rhizoctonia solani, Alternaria alternata and Fusarium oxysporum. In vitro assays showed that strain Q2-87, which has an inhibition index higher than that of other biocontrol strains (P. fluorescens strain HT5-1, FFL1R8, 2-79, Pf-5, 1M1-96, Q37-87, MVP1-4), has the strongest antagonistic activity against the three pathogens. Rhizosphere colonization experiments in the greenhouse demonstrated that strain Q2-87 colonized the roots of slash pine efficiently, and during 10-75 days the population density of Q2-87 in the rhizosphere increased from 4.36×106 CFU/g to 1×109 CFU/g (the summit value), and then decreased. In a transplantation experiment, immersing the seedling roots in a bacterial suspension of strain Q2-87 inhibited the pathogens, reduced the incidence of damping-off, and increased the survival rates of the seedlings. On day 184 after the seedlings were transplanted, the survival rate of the seedlings immersed in the suspension of Q2-87 (84%) was significantly higher than that of the control immersed in water (72.4%). In sum, P. fluorescens strain Q2-87 not only has strong antagonistic ability against the damping-off pathogens of slash pine, but also raises the seedling survival rates to attain the effect of preventing disease and promoting growth.